1. Field of the Invention
This invention relates to the field of digital recording and more particularly to an improved recording medium for use in digital magnetic recording and to circuitry for providing numerical track address information from digital information on a recording medium.
2. Description of the Prior Art
In data recording, and in magnetic data recording wherein a plurality of tracks are utilized to store information on a peripheral device, it is required that the track address be recorded so that information can be stored and retrieved from an identifiable location. In many types of digital data storage peripheral devices such as disk drives, the location information for the stored data is located on the same surface as the data being stored and in sectors, this being generally referred to in the art as utilizing embedded servo technique since the identification of the track, as well as other information such as the sector number, track number and head number, are recorded on the media preceding each portion of the disk in that sector which is set aside for recording user data. The identity of the track over which the magnetic recording head is located is required for storing and retrieving data since the host computer to which the peripheral device is connected will command that information be stored or retrieved from a specified location. In addition, in modern disk drives, when the drive is powered down the magnetic recording head is moved to an area where data is not stored and thus when a drive is started from rest position, the actuator is not located over a recording track and the head must be moved over a recording track, the head location must then be read and processed to provide the disk storage subsystem with the location of the head as a reference point for use in storing or retrieving information based on commands from the host computer.
One approach used in the prior art of providing track address information is illustrated in U.S. Pat. No. 4,424,543 entitled "Method and Apparatus for Recording Transducer Positioning Information", issued to Lewis et al. Jan. 3, 1984. In the Lewis et al. patent, tracks on the magnetic recording medium are grouped in bands of sixteen-each, with each track within a band being numbered 0 through 15. Identification of tracks within a band are written on the disk directly in Gray code without being encoded as is done in many prior art systems. With the approach illustrated in Lewis et al., it is only possible to tell which track within a band has been found and the absolute track address is not obtainable directly from the information on the track over which the head is then positioned. Other information must be utilized to identify the absolute track address. Another disadvantage with the Lewis et al. type of track address identification system is that a data separator, also sometimes referred to as a phase-locked-loop, is required and prior to reading the track address from the disk the data separator must be synced by a signal recorded ahead of the track address in the sector. This not only takes additional space from the disk which could otherwise be devoted to storage of user data, it also requires additional circuitry.
Another approach utilized to provide track address information in an embedded servo system as illustrated in U.S. Pat. No. 4,669,004 to Moon et al., issued May 26, 1987, and entitled "High Capacity Disk File with Embedded Sector Servo". In Moon et al., the track address is written in each of four burst signals located at different radial positions to eliminate need for phase coherence for each of the tracks on the disk and is encoded in a 1, 7 recording code. In addition, immediately preceding the track address information in each of the burst signals is a burst preamble and sync signal which is required to synchronize the data separator in order to decode the track address information. In the Moon et al. device, the user data is also encoded in the 1, 7 recording code. The Moon et al. system has the disadvantage of requiring a data separator, as well as requiring space on the disk for a signal to synchronize the data separator. In addition, upon start-up of the drive when the head is located over a track which is yet unidentified, the problem arises of distinguishing the track address information from user data since both are recorded on the disk in the same recording code.